CRISPR/Cas9 technology generated a GGG to CGC change in exon 6 resulting in a glycine to arginine gain of function mutation at amino acid 203. Subsequent analysis revealed that an unexpected mutation occurred that changes two bases 13 and 14 bp upstream of the designed G203R mutation. This converts the AGG at the splice acceptor site on exon 6 to an AAA that does not splice correctly. RT-PCR analysis and sequencing showed that there was virtually no correctly spliced mutant Gnao1 RNA that contained the G203R mutant allele.